Cool, followed all instrucutions and when trying to set the auto register otpion in a group with 0 message (so any new user will be registered to this group after confirmed), they system gives me an error "A group, with auto-subscribe, cannot have "moderator" permissions"

Sorry, a user can only register an email address in your user account. How to activate them, you should go: Control Painel ->> Users and Groups ->> Inactive users ->>Select the users that are next to, and activate.